Weapon sights are devices used to assist aiming weapons, such as rifles, by eye. An optical weapon sight is a device that allows the user to see the image of an aligned aiming point in the same focus as the target. Optical weapon sights include telescopic sights (or “riflescopes”) and reflector sights (or “reflex” sights).
A telescopic sight can also magnify the target image. This enables the shooter to aim at distant targets with high accuracy. In a telescopic sight, the “point of aim” is usually designated by a reticle or cross hairs. In addition, telescopic sights are also equipped with control knobs for elevation (up-down) and windage (left-right) adjustments. These knobs allow for precise vertical and horizontal movement of the reticle so that the sight's point of aim is aligned with the weapon's “point of impact”.
To use a telescopic sight, the shooter must look through the sight's eyepiece such that his eye pupil is aligned with the sights's optical axis. In addition, to see the full field of view, he has to position his eye at a set distance behind the eyepiece. This distance is called “eye relief”. In most telescopic sights used for hunting, eye relief is about 10 cm or 4 inches. The concepts of exit pupil and eye relief are well-known in the art and are described in most riflescope manufacturers' catalogs.
When a riflescope is mounted on a rifle, its optical axis will be positioned higher than the optical axis of the rifle's open sights. Therefore, to aim through his riflescope, the shooter has to raise his head from the position he would otherwise uses if he were aiming with the open sights. This situation is illustrated in FIG. 1(a). The required shift in head position is more pronounced when the riflescope has a large objective lens which necessitates a high mount. For instance, a riflescope with a 56 mm objective lens requires at least 30 mm clearance between its optical axis and the rifle's receiver top surface. A high riflescope mount is also required on certain bolt-action rifles (e.g. the famous Mauser M-98) to allow for the bolt to operate freely.
To help the shooter align his eye with the optical axis of a high-mounted riflescope, some rifle stocks are equipped with a raised or adjustable comb (see FIG. 1(a)). However, a raised comb spoils the natural lines of the rifle stock. A raised comb also make the rifle unsuitable for use with open sights.
U.S. Pat. No. 4,582,400 issued to Lewis E. Lough and assigned to the United States of America as represented by the Secretary of the Army recognizes the need for lowering the eyepoint of large night sights and subsequently discloses “A periscopic eyepiece attachment connected to a telescopic night sight mounted on a small caliber weapon to move the line-of-sight of the telescopic night sight to the line-of-sight required for the day sight (iron sights) of the weapon.” However, the solution disclosed in this patent is only applicable to certain night-vision sights when a large shift in the eyepoint is needed. It also requires two mirrors and a plurality of additional lenses to operate. What is needed is a telescopic sight with offset eyepoint such that the shooter can view the full field of view from a position below the objective optical axis.
Another situation where an optical sight with an offset eyepoint becomes desirable is when a secondary sight (often a non-magnifying reflector sight) is mounted on the top of the main telescopic sight (See FIG. 1(b)). This configuration is very useful in combat situations where a soldier needs to engage enemy positions at both close and far distances in quick succession. A soldier can use the non-magnifying reflector sight for engaging targets at close distances. Reflector sights have wide field of view and no pre-set eye relief. This makes them ideal for aiming at close-range and/or moving targets. The telescopic sight is used to aim at distant targets.
A major drawback of the configuration shown in FIG. 1(b) is that the telescopic sight and the reflector sight require two separate eye positions. U.S. patent application Ser. No. 13/843,445 filed by Quint Crispin on Mar. 15, 2013 discloses a telescopic sight which features a zig-zag optical path to facilitate using it in combination with a reflector sight. However, this solution requires that the objective is mounted on the side of the weapon which causes issues with ballistic trajectory compensation. It also has an odd zig-zag shape which is suitable for mounting on specific combat rifles only. What is needed is a telescopic sight which is mounted on the top of a weapon in a conventional manner yet does not require the soldier to change his eye position when switching his gaze from the reflector sight to the telescoping sight and vice versa.